I think I would ask ATC (or even tell them what I’m going to do) after the descent has been set up. Having experienced offsets of 20nm and greater in the PRC, you could easily fly into a military area, into another airway or, even worse, compromise your terrain clearance being so far off flight plan. Several of the Chinese routes we fly on have oxygen critical points and seriously high ground, with escape procedures not compatible with a 5nm offset, or a 30deg turn for that matter...